Process of surface plating of metals with alloys



April 23, 1935. FlEDLER PROCESS OF SURFACE PLATING OF METALS WITH ALLOYS\w w 5 Q? QN ---nnn m QN sw i -F ATTORNEYS Patented Apr. 23, 1935 UNITEDSTATES PROCESS OF SURFACE PLATING OF METALS WITH ALLOYS Marcell nearer,Bound Brook, N. J.

Application September 11, 1930, Serial No. 481,160

In Canada April 9, 1929 11 Claims.

This invention relates to surface plating or coating of one metal oralloy upon another and has for its object, more particularly, theprocess by which said coating is accomplished, and the l securing of afirmer bond between the base metal and the coating. The application is acontinuation in part of my copending application Ser.

No. 274,162 filed April 30, 1928.

An object of the invention isthe production of a composite metal articlehaving a base of one metal and a coating of another with an alloy ordiffusion zone of the two metals therebetween and one of the advantagesis the economy to be derived by my process in the saving of energy bythe use of high frequency electric currents which produce an intenseheat on the surface of the metal being coated, and also in the coatingmetal to cause rapid diffusion therebetween and so that the temper orother characteristics of the base metal are not detrimentally affected.

Another object of the invention is to apply the heat of high frequencyinduction currents to the meeting line of the base and coating metal soas to bring about a diffusion or alloying of the two metals, whilelimiting and controllingthe exposure of heat to thereby preventadversely affecting the temper, tensile strength etc., of the base'metal.

A still further object is to produce a surface plating or coating of analloy of a high chemical, and mechanical, quality upon a base metal oflower quality, thereby greatly improving the life and usefulness of thebase metal and at the same time effecting considerable saving in thesubstitution of inexpensive material for the inner body portion of ahigh grade material. In some cases where the mechanical strength isimportant, we can have a base of cast iron or steel and cover it withchromium or nickel, for instance; we not only have the-skin of the metalmore resistant to corrosion or chemicals, butwe have on the inside theoriginal steel which is strong and cheap and is substantially unaffectedby the heat treatment.

These and other objects will appear as I relate the process in detailsof which the following is a specification.

In the drawing which shows a diagrammatic form of embodiment ofapparatus suitable for practicing my invention,

Figure 1 is a part sectional view of one form of furnace suitable fortreating pipe tubing and bars according to my process.

Figure 2 is an enlarged or magnified diagrammatic cross section of acoated metal article before heat treatment.

Figure 3 is a view similar to Figure 2 after heat treatment.

The base metal to be coated or. plated is first 5 covered with anothermetal by spraying, dipping, plating or the like, preferably with onewhich will compose an alloy or eutectic or chemical compound with thebase metal, and it is then treated in an electric induction furnace, thetem- 1o perature being raised to the required degree necessary to causethe metals to diffuse together at their meeting line.

It is a well known fact that the higher the frequency of the eddycurrents induced in a body 15 of conducting material the more pronouncedwill be the skin' heating effect. This fact may be made use of in myprocess in which the greatest intensity of heat may be generateddirectly at the surfaces or interface of the base and coating 20 metalby using as high a frequency as permissible, causing the metals to fuseinto an alloy at the meeting line of the base and coating metal withoutpermitting penetration of the heat to the inside part or body part whichis kept practically 25 cold, except at the surface or skin whereby thetemper of the base or body metal remains substantially unaffected. Thepenetration of heat into the base or body part may be further limited bymoving the pieces rapidly through the 30 zone of the heating coil or byartificially cooling the one side of the base or body part by a currentof air, water, or other suitable cooling medium. However, in mostinstances the extremely high frequencies needed to produce such ex- 35treme skin effect are not necessary. Frequencies of a lower order ofmagnitude, but high as compared with ordinary 60-cycle current, e. g.960- cycles, may be used with equally satisfactory results. Withfrequencies of such lower order of 40 magnitude the heating is veryrapid, and while the base may, and usually will, be heated throughoutthe exposures necessary are so short that the properties of the base arenot detrimentally affected. Therefore for most purposes the skin effectof extremely high frequencies is not necessary in thepractice of thisinvention. In the drawing, I8 indicates a piece of pipe or tubingundergoing treatment. This pipe is preferably of a material ofrelatively high strength such as iron or steel but may be formed ofcopper, brass or any other suitable material. A coating l8a of chromium,nickel, cobalt, or other alloying material is formed on the surface ofthe tube I 8 by spraying, dipping, electroplating or the like to form asolid substantially uninterrupted coating giving a continuous mechanicalas well as an uninterrupted electrical conducting wall, and the coatedtube is passed through the coil 20 of a high frequency inductionfurnace. The coil 20 is preferably water cooled as indicated at 20b andthe tube I8 is shielded by a quartz or other chamber 20a having endclosures 20d which form a wiping fit with the tube [8 which permits theuse of a neutral or deoxidizing atmosphere within the chamber 20a, ifdesired. Rolls 200 are provided for moving the tube l8 rapidly throughthe furnace, and telescoping air or water spray nozzles 2| may beprovided to spray the inside of the tube with a cooling medium.

For example, a base metal of iron or steel coated with nickel orchromium by electroplating or dipping when subjected to an inductioncurrent of 1500 cycles for 4 seconds, the skin effect is sufficient tocause diffusion or alloying of the base and coating layer withoutsoftening or otherwise adversely affecting the mechanical properties ofthe entire article.

Figure 2 shows the base 18 and coating lBa before passing through thezone of the furnace in which the coating forms a substantially uniformline on the surface of the base. Figure 3 shows the same section afterpassing through the zone of the furnace in which it will be noted thatthe coating and base metal have diffused together along the meeting line[8b forming a strong interlocked bond which will prevent separation ofthe base and coating metal even under such severe conditions as areinduced by repeated heat- -ing and cooling and which will protect thebase from corrosion. At the same time it will be noted that the grainstructure of the base has not been materially disturbed, and the temperand strength of the base has not been materially affected, due to theshort time the metal is in the heating zone.

In treating a steel tube having an outside diameter of one (1) inch anda wall thickness of one-sixteenth g) inch, with a chromium plate 0.0002inch in thickness in a furnace having a power input of 22-23 K. W. and acoil of five and one-half (5 /2) by one and five-eighths (1%) incheswith a frequency of 30,000 cycles per second, the optimum diffusion oralloying is secured when the tube is fed through the coil at a rate of0.4 to 0.55 inch per second. A 300 K. W. input and only 500 cycles persecond will cause the same effect when the tube is passed through thecoil of a speed of five (5) inches per second. The frequency may belowered as the input is increased, the higher the frequency however, thehigher the skin effect and the lower the degree of heating of the entirebody portion. The speed at which the tube is passed through the furnacealso limits the penetration of the heat into the body of the tube.

In order to make coated articles of desired composition, layers of thedifferent metals may be placed on the base metal and fused. Forinstance, a cast iron base is first chromium plated then cobalt platedto produce a chromium-cobalt-iron alloy on the surface of the cast ironbase.

It might be remarked that the coating is of a more uniform compositionthe thinner the layers of the covering are. In cases where the firstmetal applied is of a lower melting point than the base, for instance,zinc base plated with bismuth or cadmium and then copper plated on top,

will give a zinc-bismuth-copper alloy or zinccadmium copper alloy.

In case the applied covering metals and the base metal do not alloyreadily, but one material only penetrates into the other one, then weuse this process only to let one metal penetrate into the other one andwe may heat treat it in any regular furnace to secure the desiredalloying.

While it is preferable to use a high frequency alternating current toproduce the skin heating of the metal, it is possible also to use aninterrupted direct current in which the interruption is at asufficiently high frequency. The process may be used for treating tubes,plates or irregularly shaped articles by shaping the coil in a circle,fiat spiral or the like to conform to the shape of the article and focusits induced currents on the surface thereof.

Various modifications and changes may be made in the specific examplesand apparatus shown, which are intended only to illustrate and not limitmy invention, without departing from the spirit of my invention, or thescope of the appended claims.

I claim:

1. The method of causing penetration or diffusion of one substance intoa metal base which comprises heating the skin of said metal base to adiffusion temperature in the presence of the penetrating substance .bythe use of an induced high frequency current without heating the entirebody of said metal base or affecting its temper, while artificiallycooling the one side of the metal base to limit penetration of the heatinto the bodyof themetal base.

2. The method of causing diffusion of one metal into the surface ofanother metal while applying the heat to the meeting surface of themetals which comprises bringing the metals into contact and subjectingthe meeting surface of the metals to the heat of a high frequencyinterrupted current in a furnace while moving the metals rapidly throughthe furnace to cause heating of the skin only of said metals andartificially cooling one side of said metals.

3. The method of forming a non-corrosive surface on a base metal tubewhich comprises coating the tube with a non-corrosive metal and passingthe coated tube through the coil of a high frequency induction furnaceto cause diffusion of the coating and base together atthe meeting lineand artificially cooling the tube to limit penetration of the heatthereunto, the movement of the tube through the coil being such that nostructural change occurs in any other part of the base.

4. A method of adherently bonding a coating metal to a metallic base,comprising providing said base with a coherent layer of the coatingmetal, subjecting the coated base to a high frequency electrical fieldand thereby heatng the coating and the underlying base by high frequencyelectric currents induced therein, and continuing such heating for sucha time as to cause adherent bonding diffusion between the coating andthe base. 7

5. A method of adherently bonding a chromium coating to a ferrous metalbase, comprising providing said ferrous base with a coherent coatinglayer of chromium, subjecting the coated base to a high frequencyelectrical field and thereby heating the coating and the underlying baseby high frequency electric currents induced therein, and continuing suchheating for such a time as to cause adherent bonding diffusion betweenthe chromium coating and the ferrous base.

6. A continuous method of adherently bonding a coating metal to ametallic base, comprising providing said base with a coherent layer ofthe coating metal, progressively subjecting the coated base to a highfrequency electrical field and thereby locally and progressively,heating the coating and the underlying base by high frequency electriccurrents induced therein for such a time as to progressively causeadherent bonding diffusion between the coating and the base.

7. A method of adherently bonding a coating metal to a metallic base,comprising providing said base with a coherent layer of the coatingmetal, subjecting the coated base to a high frequency electrical field,regulating the electrical power input and frequency of said field andthe time of exposure of the coated base to said field to rapidly heatthe coating and the underlying base by high frequency electric currentsinduced therein, and continuing such heating for such a time as to causerapid and adherent bonding diffusion between the coating and the basewithout adversely ailectlng the mechanical properties of the base.

8. A method of adherently alloying a coating metal to a metallic base,comprising providing said base with a coherent layer of the coatingmetal, subjecting the coated base to a high frequency electrical fieldand thereby heating the coating and the underlying base by highfrequency electric currents induced therein, and continuing such heatingfor such a time as to cause alloying between the coating and the base.

9. A method of adherently alloying a chromium coating to a ferrous metalbase, comprising providing said ferrous base with a coherent layer ofchromium, subjecting the coated base to a high frequency electricalfield and thereby heating the coating and the underlying base by highfrequency electric currents induced therein, and continuing such heatingfor such a time as to cause alloying between the chromium coating andthe base.

10. A method of adherently alloying a coating metal to a metallic base,comprising providing said base with a coherent layer of the coatingmetal, progressively subjecting the 'coated base to a high frequencyelectrical field and thereby locally and progressively heating thecoating and the underlying base by high frequency electric currentsinduced therein for such a time as to cause alloying between the coatingand the base.

11. A method of adherently alloying a coating metal to a metallic base,comprising providing said base with a coherent layer of the coatingmetal, subjecting the coated base to a high frequency electrical field,regulating the electrical power input and frequency of said field andthe time of exposure of the coated base to said field to rapidly heatthe coating and the underlying base by high frequency electric currentsinduced therein, and continuing such heating for such a time as to causerapid alloying between the coating and the base without adverselyaffecting the mechanical properties of the base.

MARCEIL FIEDLER.

